You can then navigate the channels and change the various sound levels using your keyboard left, right, up and down buttons. But does this look coherent with the rest of your modern desktop? No it doesn’t, and that’s why I suggest you install and use Gnome AlsaMixer instead that looks like this:
You can set everything using your mouse and activate/deactivate or rename all channels through the preferences. Much better right?
Download and install it from your distribution’s software manager. If you can’t find it though, you may try to compile the latest version from source after downloading it from the below button.